942 research outputs found
Near-Infrared Surface Photometry of Bulges and Disks of Spiral Galaxies. The Data
We present optical and near-infrared (NIR) surface brightness and colour
profiles,in bands ranging from U to K, for the disk and bulge components of a
complete sample of 30 nearby S0 to Sbc galaxies with inclinations larger than
50 degrees. We describe in detail the observations and the determination of
colour parameters. Calibrated monochromatic and real-colour images are
presented, as well as colour index maps. This data set, tailored for the study
of the population characteristics of galaxy bulges, provides useful information
on the colours of inner disks as well. In related papers, we have used them to
quantify colour gradients in bulges, and age differentials between bulge and
inner disk.Comment: 18 pages Latex with 2 postscript figures. Accepted for New Astronomy.
This is an electronic paper; a complete preprint, including all of the tables
and figures can be found at
ftp://www.astro.rug.nl/peletier/newast/newast.htm
Upscaling of dislocation walls in finite domains
We wish to understand the macroscopic plastic behaviour of metals by
upscaling the micro-mechanics of dislocations. We consider a highly simplified
dislocation network, which allows our microscopic model to be a one dimensional
particle system, in which the interactions between the particles (dislocation
walls) are singular and non-local.
As a first step towards treating realistic geometries, we focus on
finite-size effects rather than considering an infinite domain as typically
discussed in the literature. We derive effective equations for the dislocation
density by means of \Gamma-convergence on the space of probability measures.
Our analysis yields a classification of macroscopic models, in which the size
of the domain plays a key role
An Internet Portal based on 'Twenty Questions'
An efficient Internet portal should contain a search engine or maybe even a decision support system to supply the user with the information (s)he may be looking for. In this report an intelligent agent is suggested that relates different sites to each other, based on the answers supplied by the users looking for certain information. For this purpose a self-learning system has been made, based on the neural network of the game Twenty Questions, but with a strategy that relates different objects or sites by correlating the list of answers to the questions
Thermal Modeling in Polymer Extrusion
In this paper we consider thermal effects of polymer flows through a cylindrical die. First, we derive a model for the oscillatory behavior of polymer flow in an extruder given a functional relation between the pressure and flow rate. A simple isothermal but temperature dependent model is constructed to find this relation. Unfortunately, the model is shown to be invalid in the physical regime of interest. We present several arguments to suggest that the isothermal assumption is reasonable but that a more detailed understanding of the small-scale molecular dynamics near the boundary may be required. Second, we show that a simplified model for thermoflow multiplicity in a cooled tube is inconsistent, when the stationary non-Newtonian flow is assumed to be incompressible without radial pressure gradients and without radial velocity. This inconsistency can be removed by allowing for weak compressibility effects in the down-steam area
Quantification of coarse-graining error in Langevin and overdamped Langevin dynamics
In molecular dynamics and sampling of high dimensional Gibbs measures
coarse-graining is an important technique to reduce the dimensionality of the
problem. We will study and quantify the coarse-graining error between the
coarse-grained dynamics and an effective dynamics. The effective dynamics is a
Markov process on the coarse-grained state space obtained by a closure
procedure from the coarse-grained coefficients. We obtain error estimates both
in relative entropy and Wasserstein distance, for both Langevin and overdamped
Langevin dynamics. The approach allows for vectorial coarse-graining maps.
Hereby, the quality of the chosen coarse-graining is measured by certain
functional inequalities encoding the scale separation of the Gibbs measure. The
method is based on error estimates between solutions of (kinetic) Fokker-Planck
equations in terms of large-deviation rate functionals
A consistent treatment of link and writhe for open rods, and their relation to end rotation
We combine and extend the work of Alexander & Antman \cite{alexander.82} and
Fuller \cite{fuller.71,fuller.78} to give a framework within which precise
definitions can be given of topological and geometrical quantities
characterising the contortion of open rods undergoing large deformations under
end loading. We use these definitions to examine the extension of known results
for closed rods to open rods. In particular, we formulate the analogue of the
celebrated formula (link equals twist plus writhe) for open rods and
propose an end rotation, through which the applied end moment does work, in the
form of an integral over the length of the rod. The results serve to promote
the variational analysis of boundary-value problems for rods undergoing large
deformations.Comment: 17 pages, 4 figure
Star formation in the central regions of galaxies
Massive star formation in the central regions of spiral galaxies plays an
important role in the dynamical and secular evolution of their hosts. Here, we
summarise a number of recent investigations of the star formation history and
the physical conditions of the gas in circumnuclear regions, to illustrate not
only the detailed results one can achieve, but also the potential of using
state-of-the-art spectroscopic and analysis techniques in researching the
central regions of galaxies in general. We review how the star formation
history of nuclear rings confirms that they are long-lived and stable
configurations. Gas flows in from the disk, through the bar, and into the ring,
where successive episodes of massive star formation occur. Analysing the ring
in NGC 7742 in particular, we determine the physical conditions of the line
emitting gas using a combination of ionisation and stellar population
modelling, concluding that the origin of the nuclear ring in this non-barred
galaxy lies in a recent minor merger with a small gas-rich galaxy.Comment: Invited contribution, to appear in "Mapping the Galaxy and other
galaxies", Eds. K. Wada and F. Combes, Springer, in pres
A subarcsecond resolution near-infrared study of Seyfert and `normal' galaxies: II. Morphology
We present a detailed study of the bar fraction in the CfA sample of Seyfert
galaxies, and in a carefully selected control sample of non-active galaxies, to
investigate the relation between the presence of bars and of nuclear activity.
To avoid the problems related to bar classification in the RC3, e.g.,
subjectivity, low resolution and contamination by dust, we have developed an
objective bar classification method, which we conservatively apply to our new
sub-arcsecond resolution near-infrared imaging data set (Peletier et al. 1999).
We are able to use stringent criteria based on radial profiles of ellipticity
and major axis position angle to determine the presence of a bar and its axial
ratio. Concentrating on non-interacting galaxies in our sample for which
morphological information can be obtained, we find that Seyfert hosts are
barred more often (79% +/- 7.5%) than the non-active galaxies in our control
sample (59% +/- 9%), a result which is at the 2.5 sigma significance level. The
fraction of non-axisymmetric hosts becomes even larger when interacting
galaxies are taken into account. We discuss the implications of this result for
the fueling of central activity by large-scale bars. This paper improves on
previous work by means of imaging at higher spatial resolution and by the use
of a set of stringent criteria for bar presence, and confirms that the use of
NIR is superior to optical imaging for detection of bars in disk galaxies.Comment: Latex, 3 figures, includes aaspptwo.sty, accepted for publication in
the Astrophysical Journa
- …